1. Field of the Invention
The present invention relates to an information storage medium having a super-resolution structure and an apparatus to record and/or reproduce the same, and, more particularly, to a super-resolution information storage medium designed to prevent degradation of a reproduction signal after repeated reproduction and an apparatus to record and/or reproduce from the same.
2. Description of the Related Art
An information recording and/or reproducing apparatus performs non-contact recording/reproducing to/from an information storage medium using an optical pickup. Since the demand for high density recording has increased, research has been conducted to develop a super-resolution information storage medium having recording marks or pits that are smaller than the resolution limit of a laser beam which uses a super-resolution phenomenon. Here, it is understood that when a wavelength of a laser of an optical pickup used is λ and a numerical aperture of an objective lens is NA, the reproduction resolution limit is λ/4NA.
The super-resolution information storage medium has a super-resolution reproduction layer from which marks or pits that are smaller than the resolution limit of a reproducing beam are read using a super-resolution phenomenon. A laser beam focused onto an information storage medium has an approximately Gaussian intensity distribution. Thus, when the information storage medium is heated by the incident beam with the Gaussian intensity profile, a temperature distribution on a region on which a laser beam is irradiated also has an approximately Gaussian profile.
Therefore, the super-resolution reproduction layer has a high-temperature region near the center of a beam and a low-temperature region at the periphery of the beam. Reproduction of marks or pits smaller than the resolution limit may be realized by changing optical characteristics of a local region of the super-resolution reproduction layer, i.e., a super-resolution region.
Since the temperature increases toward the center of a laser beam spot, a portion of or the entire super-resolution region may melt. When the portion of or the entire super-resolution region melts, the melted super-resolution material floats away due to the rotation of an information storage medium or pressure from other layers. This effect may result in signal degradation after repeated reproduction operations.